1. Field of the Invention
The invention relates to soil fertilization with nitrogenous materials, and more particularly to the reduction of ammonia volatilization losses during such fertilization.
2. Description of the Art
Among the chemical fertilizer materials commonly used in agriculture, nitrogen fertilizers are applied in the largest quantities. Most commercial fertilizers contain all, or a large part, of their nitrogen values in the ammoniacal form, e.g., as ammonium sulfate, ammonium nitrate, ammonium phosphate, urea, aqueous ammonia, and the like.
It has long been known that these ammonic fertilizers, when applied to the soil, experience losses of nitrogen content due to the volatilization of ammonia. The losses are significant, particularly when the fertilizer is applied to the surface of the soil, sometimes approaching 100 percent of the originally contained ammonia under the most adverse soil and climatic conditions. Urea has been thought to be particularly susceptible to volatilization loss.
The ammonia volatilization loss problem has been addressed in U.S. Pat. No. 3,232,740 to Sor et al. and U.S. Pat. No. 3,388,989 to Sor. In these patents, the mechanism of loss from urea is shown to involve hydrolysis of urea to ammonium carbonate, under the influence of urease enzyme, and decomposition of the ammonium carbonate into ammonium bicarbonate and free ammonia. Up to about 50 percent of this ammonia is said to be absorbed by soils, with the remainder lost by escape into the air. A partial solution to the problem, according to the patents, lies in deactivating urease with an "inhibitor", such as an organo-urea compound, formaldehyde, or a boron, fluorine or heavy metal compound. By incorporating an inhibitor into urea particles, some reduction in ammonia loss was demonstrated.
Another approach to minimizing the losses is shown in my U.S. Pat. No. 4,073,633, wherein combinations of urea and acid generating compounds are applied to the soil. The acid generators reduce soil pH in the immediate vicinity of the basic urea particles, decreasing the amount of free ammonia which forms and thereby preventing volatilization.
A need remains, however, for a means to reduce the ammonia volatilization from surface-applied fertilizers which is applicable to all ammonic materials, and which does not require inordinately expensive chemical additives. Such means would help to make surface application of solids attractive, for example, in cases where large or inaccessible areas (such as forests) are to be fertilized by aerial application. Also, the surface application of liquid or suspension ammonic fertilizers would be made more feasible if ammonia volatilization could be reduced.
Accordingly, it is an object of the present invention to provide an improved method for the surface application of ammonic fertilizers.
A further object is to provide a method for the surface application of ammonic fertilizer, which reduces the loss of plant nutrient value from ammonia volatilization.
Another object is to provide fertilizer compositions which will not be subject to excessive ammonia volatilization losses when used in surface applications to soils.
These, and other objects, will appear to those skilled in the art, from consideration of the following description and claims.